A vital step in the sewage treatment process at the Western Treatment Plant (WTP) is nitrogen removal, needed to reduce nutrients discharged to Port Phillip Bay.
Conventional nitrogen removal uses bacteria that require large quantities of oxygen and carbon – and consequently has a high-energy demand. Recent work has revealed methods for shortcutting the nitrogen removal process, which greatly reduces both the oxygen and carbon needed. Potentially the ‘next big thing’ in domestic sewage treatment, shortcut nitrogen removal has the potential to transform the way we treat wastewater, and provide cost savings for Melbourne Water and our customers.
Cultivating the right bacterial population, however, is not simple science. Although shortcut nitrogen removal is well established in Europe and the USA for digester sidestream processing, it is only just starting to be implemented for treating the whole sewage flow. As WTP does not have a digester with a nutrient-rich side-stream, we face a number of challenges before the process can be used at the plant, and to this end we have embarked on a series of trials.
Working with Victoria University, four workbench-sized bioreactors were set up in a laboratory and successfully cultivated specific bacteria (anammox) over a period of 18 months. Following these trials, Melbourne Water worked with Jacobs, John Holland and Barwon Water to construct a demonstrationscale plant for trialling the full shortcut process. This demonstration plant is one of the first of its kind in the world and is attracting global interest across the industry. Lessons learned from the trial have the potential to be implemented at both the Western and Eastern treatment plants.
While preliminary results are showing growth of the right bacteria, operations will continue throughout 2018 to build confidence that the process will work under a range of conditions.